Currently, marginal energy, or peak energy, is produced mainly by gas turbine engines, operating either in a simple cycle or a combined cycle configuration. As a result of load demand profile, gas turbine engines are cycled up during periods of high demand and cycled down, or turned off, during periods of low demand. In many areas of the world, less efficient simple cycle gas turbine engines are used instead of more efficient combined cycle gas turbine engines. This is due to the lack of available water typically required for combined cycle plant operation and high peak loads. Furthermore, even in areas of the world with high demand for more power, simple cycle gas turbines are often used due to high fuel prices.
The Applicant has developed and produced an air injection system, commonly referred to as TurboPHASE®, which is capable of increasing the base load and peak load capacities of new and existing gas turbines while also improving efficiency. Applicant's air injection system, when applied to a fleet of gas turbines operating on liquid fuel would result in a fleet efficiency improvement of 3% during off peak periods and 5% during peak periods. However, one significant challenge for the air injection system is air cooling the system at power plants that do not have water.
The air injection system utilizes an internal cooling circuit for cooling the major components of the air injection system, including a fueled engine, an intercooled multistage compressor, and a lube oil system. Typically, a water glycol system cools each of the components with a dedicated heat exchanger that is internal to the air injection system. One challenge is to develop a cooling system for the air injection system that also works in hot climates, as traditional intercooled compressors utilize a water cooling system.
One key element of the air injection system is the modular nature of the system. The air injection system typically has a footprint, or occupying space, of a standard 40 foot shipping container or less, making it very easy logistically to install or move to an alternate location. Furthermore, the ancillary equipment required to support the air injection system, including air piping, air vent valves, air injection valves, recuperator, silencers, auxiliary air supply system and the gas fuel control system is typically mounted on the roof of the air injection system, so as to maintain the overall footprint of the system and its modular nature.
Applying air cooling systems to an intercooled compressor introduces challenges due to the low temperature desired by the intercooling process. As one skilled in the art can appreciate, the lower the coolant temperature available for intercooling a multistage compression process, the more efficient and less power the multistage intercooled compressor requires for the same air flow and pressure output. On a fueled engine, the coolant temperature on the hot side of the heat exchanger, inside the radiator, is typically about 200 degree Fahrenheit (deg. F.) and the air temperature outside, even in desert-type conditions is much cooler, resulting in a large thermal gradient to promote heat transfer to the air. Therefore, a radiator type cooling system for the engine works extremely well and is minimal size, even in extremely hot conditions. However, intercooling coolant temperatures are typically 80 deg. F. to 100 deg. F. and are typically cooled with water from open cooling towers or a natural water source such as from large water bodies like lakes, rivers or oceans. These water coolant sources are typically cooler than ambient air conditions, and even in extremely hot ambient conditions, can typically provide cooling sufficient to meet the 80 deg. F. to 100 deg. F. requirement. The maximum temperature of about 100 deg. F. is critical because this coolant is not only used to cool the interstage air as it is compressed, but it is typically used to cool the lube oil system in the compressor, which typically has a temperature limit of about 130 deg. F.